Figure 2.
Selectively bred bHR and bLR rats model an extreme propensity for internalizing vs. externalizing behavior. (A) Over the course of 56 generations of selective breeding (F1–F56), the bHR rats (green) have developed increasingly elevated exploratory activity in a novel field (y-axis: average total locomotor score), whereas the bLR rats (red) have become less exploratory. These trends plateaued after F42, when our breeding strategy changed to deaccelerate divergence. Arrows indicate the generations during which hippocampal transcriptomic profiling datasets were collected along with a name indicating the respective laboratory, platform, and generation for each dataset. (B) bLR rats have been highly anxious since the initiation of our breeding colony. The example above is from the behavioral data accompanying the MBNI_RNASeq_F37 transcriptomic dataset showing bLRs spending a smaller percentage of time in the anxiogenic open arms of the elevated plus maze than cross-bred (bHRxbLR) bIR rats or bHR rats (effect of phenotype: F2,15 = 6.72, p = 8.25 × 10−3; boxes = first quartile, median, and third quartile; whiskers = range or 1.5× the interquartile range; dot = outlier datapoint falling beyond the whiskers of the boxplot). (C) bLR rats are more reactive to stressors. This example is from the behavioral data accompanying the MBNI_RNASeq_F43 transcriptomic dataset showing bLR rats spending a smaller percentage of time interacting socially following exposure to a single mild stressor in the form of a brief exposure to the anxiogenic open arms of the EPM (F1,8 = 5.86, p = .0418, boxplot follows the conventions of panel B). bHR, bred high-responder; bIR, bred intermediate-responder; bLR, bred low-responder; EPM, elevated plus maze.